Cell cycle notes

Cells spend about 90% of the cycle in interphase preparing for division across three sub-phases.

• G1 Phase (First Gap). The cell grows physically larger, copies organelles, and builds proteins needed for everyday functions.

• S Phase (Synthesis). The cell duplicates its entire nuclear DNA and copies its centrosomes so each future cell gets a complete genome.

• G2 Phase (Second Gap). The cell finishes growing, stores energy, and makes microtubules to assemble the mitotic spindle.

• (Nuclear Division)

  • Prophase. Loose chromatin packs tightly into visible chromosomes, the nuclear membrane dissolves, and spindle fibers extend from centrosomes moving to opposite ends of the cell.

  • Metaphase. Spindle fibers attach to chromosome centromeres and line the chromosomes up down the middle of the cell at the metaphase plate.

  • Anaphase. Sister chromatids separate and get pulled toward opposite poles of the cell as spindle fibers shorten.

  • Telophase. New nuclear envelopes form around each set of chromosomes at both poles, and the DNA uncoils back into chromatin.

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